sábado, 7 de novembro de 2009

The massive eruption of the Thera volcano in the Aegean Sea more than 3,000 years ago produced killer waves that raced across hundreds of miles of the Eastern Mediterranean to inundate the area that is now Israel and probably other coastal sites, a team of scientists has found.

The team, writing in the October issue of Geology, said the new evidence suggested that giant tsunamis from the catastrophic eruption hit “coastal sites across the Eastern Mediterranean littoral.” Tsunamis are giant waves that can crash into shore, rearrange the seabed, inundate vast areas of land and carry terrestrial material out to sea.

The region at the time was home to rising civilizations in Crete, Cyprus, Egypt, Phoenicia and Turkey.

For decades, scholars have suggested that the giant eruption, just 70 miles from Crete, might have brought about the mysterious collapse of Minoan civilization at the peak of its glory. The remnants of Thera’s eruption today make up a circular archipelago of volcanic Greek isles known as Santorini.

Thera is thought to have erupted between 1630 and 1550 B.C., or the Late Bronze Age, a time when many human cultures made tools and weapons of bronze. Scholars say the tsunamis and dense clouds of volcanic ash from the eruption had cultural repercussions that rippled across the Eastern Mediterranean for decades, even centuries. The fall of Minoan civilization is usually dated to around 1450 B.C. Geologists judge the eruption as far more violent than the 1883 eruption of the volcanic island of Krakatoa in Indonesia, which killed more than 36,000.

The team did its excavations off Caesarea, Israel, a coastal town dating from Roman and Byzantine days. The coastal region was only sparsely settled at the time of the Thera eruption, with no identifiable city.

The team sank a half-dozen tubes into the offshore seabed and pulled up sediment cores for analysis. It looked for standard signs of tsunami upheaval, including pumice (the volcanic rock that solidifies from frothy lava), distinctive patterns of microfossils, cultural materials from human dwellings and well-rounded beach pebbles that seldom appear in deeper waters.

Writing in Geology, a journal published by the Geological Society of America, the team reported finding evidence of three tsunamis — two historically documented ones dating to A.D. 115 and 551, and one from the time of the Thera eruption.

The Thera tsunamis, the team wrote, left a signature layer in the seabed of well-rounded pebbles, distinctive patterns of mollusks and characteristic inclusions in rocky fragments all oriented in the same direction.

The disturbed layer, up to 16 inches wide, came from a few feet below the seabed in waters up to 65 feet deep.

“These findings,” the team wrote, “constitute the most comprehensive evidence to date that the tsunami event precipitated by the eruption of Santorini reached the maximum extent of the Eastern Mediterranean.”

The team added that, if the giant waves were big enough to reach Israel, “then presumably other Late Bronze Age coastal sites across the Eastern Mediterranean littoral will likely have been affected as well.”

A version of this article appeared in print on November 3, 2009, on page D3 of the New York edition.